Migration of ionic and nanoparticulate zinc from nanocellulose/ZnO nanoparticle films: morphology-dependent behaviour...

The incorporation of zinc oxide nanoparticles (ZnO NPs) into biopolymers has gained attention for active food packaging due to their antimicrobial properties. However, potential Zn migration associated with safety concerns remains underexplored, particularly in non-regulated bio-based polymers. In this study, Zn migration from nanocellulose (NC) films incorporating spherical-, flower- and sheet-shaped ZnO NPs was evaluated, in ionic and nanoparticulate forms. Migration tests were conducted using water and ethanol 10% as food simulants under different time-temperature conditions. Zinc release was quantified using complementary analytical and microscopic approaches, and Fick's second law and Weibull models were employed to describe the migration kinetics. Migration behaviour was influenced by nanoparticle morphology, simulant type, and temperature. Zinc migrated predominantly as Zn²⁺, with minimal nanoparticle contribution, although distinction from cellulose fibres proved challenging. NC films containing flower-shaped nanoparticles exhibited the highest Zn migration, yet migration levels for all films remained below the European specific migration limit. Water promoted higher migration than ethanol, and unexpectedly, Zn migration was lower at 60 °C compared to 23 °C, likely due to matrix effect. Fickian fits yielded diffusion coefficients in the range 10^-16-10^-15 m² s^-1, while Weibull β < 1, confirmed diffusion-controlled release. These findings confirm the potential of NC/ZnO nanocomposites for food packaging applications and highlight the importance of combining multi analytics with kinetic modelling to support safety assessment.